The preparation of sodium bicarbonate and ammonium sulfate has been discussed at length in the prior art. One of the most recent patents regarding this technology is Canadian Patent No. 2,032,627, issued Jan. 14, 1997 to Thompson et. al.
This reference teaches a process for producing sodium carbonate and ammonium sulfate from naturally occurring sodium sulfate. The reference is also concerned with the preparation of a double salt of sodium and ammonium sulfate. This is a source of contamination when one is trying to form reasonably pure ammonium sulfate and the presence of any double salt and sodium in an ammonium sulfate product does nothing other than reduce the value of the ammonium sulfate to a non-commercial product. In the methodology, it is clearly stated on page 13, beginning at line 8:
" . . . the brine remaining after screening off the solid sodium bicarbonate contains a mixture of unreacted sodium sulfate, ammonium sulfate, ammonium bicarbonate and minor amounts of sodium bicarbonate. This brine is transferred by a pump 36 into a gas recovery boiler 31 where it is heated to a temperature of 95.degree. to 100.degree. C. Under these conditions, the ammonium bicarbonate breaks down and sodium bicarbonate dissolved in the brine reacts with ammonium sulfate to produce sodium sulfate, carbon dioxide and ammonia. Carbon dioxide and ammonia dissolved in the brine boil off, leaving in the solution a mixture composed mostly of sodium and ammonium sulfate. The carbon dioxide and ammonia so regenerated are cooled in a gas cooler 32 and returned to the reactor 21 by a blower 33 after being further cooled in a gas cooler 34. This regeneration step minimizes the amount of carbon dioxide and ammonia used in the process." PA1 "If, instead of precipitating the double salt in the first stage of the process, it is preferred to precipitate ammonium sulfate, the following procedure may be adopted. PA1 Referring now to FIG. 10, it will be seen that each of the three curves which divide this figure into three parts corresponds to the simultaneous precipitation of two salts. PA1 At any given temperature, the point representing a system may be vertically displaced by removing some of the water from the solution. In order to precipitate ammonium sulfate instead of the double salt, it is necessary to operate at a temperature greater than that at the triple point, i.e., about 59.degree. C. PA1 The point A, which corresponds to about 63.degree. C. is suitable, since it is sufficiently distant from the triple point to avoid unwanted precipitation of the double salt without requiring too much heat. PA1 It is clear that at the point A, there is simultaneous precipitation of sodium sulfate and ammonium sulfate, but this is in the form of a mixture of the two salts rather than as a double salt." PA1 " . . . From the foregoing it will be seen that the process according to the invention may be carried out by precipitating the ammonium sulfate in the form of the double salt, or as (NH.sub.4).sub.2 SO.sub.4 simultaneously with sodium sulfate, or by precipitating it simultaneously in the form of ammonium sulfate and in the form of the double salt." PA1 a) precipitating, in at least one precipitation operation, sodium bicarbonate precipitate to increase the concentration of ammonium sulfate in solution while reducing the concentration of sodium bicarbonate in the solution; PA1 b) centrifuging and washing the sodium bicarbonate precipitate to convert the precipitate to industrial grade sodium bicarbonate; PA1 c) saturating the solution from step a) with one of sodium sulfate or ammonium bicarbonate by addition of the sodium sulfate or the ammonium bicarbonate to the solution at a temperature of between 35.degree. C. and 50.degree. C. to form a second precipitate of sodium bicarbonate; PA1 d) conditioning the solution from step c) by at least one of heating the solution to 95.degree. C. to liberate ammonia and carbon dioxide and contacting the solution from step c) with sulfuric acid to degas any carbonate minerals; PA1 e) cooling solution from step d) at a temperature between -2.degree. C. and 2.degree. C. to form a third precipitate of sodium bicarbonate; PA1 f) recycling precipitates from steps d) and e) to step a); PA1 g) treating solution from step e) with sulfuric acid to degas any remaining carbonate minerals from sodium bicarbonate and reducing the sodium sulfate to less than 7% by weight; and subsequently PA1 h) recovering purified ammonium sulfate solution. PA1 a) precipitating, in at least one precipitation operation, sodium bicarbonate precipitate to increase the concentration of ammonium sulfate in solution while reducing the concentration of sodium bicarbonate in the solution; PA1 b) centrifuging and washing the sodium bicarbonate precipitate to convert the precipitate to industrial grade sodium bicarbonate; PA1 c) saturating the solution from step a) with one of sodium sulfate or ammonium bicarbonate by addition of the sodium sulfate or the ammonium bicarbonate to the solution at a temperature of between 35.degree. C. and 50.degree. C. to form a second precipitate of sodium bicarbonate; PA1 d) conditioning the solution from step c) by at least one of heating the solution to 95.degree. C. to liberate ammonia and carbon dioxide and contacting the solution from step c) with sulfuric acid to degas any carbonate minerals; PA1 e) cooling solution from step d) at a temperature between -2.degree. C. and 2.degree. C. to form a third precipitate of sodium bicarbonate; PA1 f) recycling precipitates from steps d) and e) to step a); PA1 g) heating the solution from step e) to a temperature of 95.degree. C. to convert residual sodium bicarbonate to sodium sulfate and release ammonia and carbon dioxide for recycle; and subsequently PA1 h) recovering purified ammonium sulfate solution. PA1 a) providing a solution of sodium sulfate; PA1 b) contacting the sodium sulfate solution with carbon dioxide and ammonia or ammonium ions to form a first precipitate of sodium bicarbonate and a solution containing ammonium sulfate; PA1 c) progressively precipitating sodium bicarbonate from the solution to increase the concentration of ammonium sulfate and reduce the concentration of sodium bicarbonate in the solution; PA1 d) recovering as a product the first precipitate of sodium bicarbonate; PA1 e) centrifuging and washing the first precipitate of sodium bicarbonate to convert the sodium bicarbonate into industrial hygrade sodium bicarbonate; PA1 f) treating solution remaining from d) with sodium sulfate at a temperature of between 35.degree. C. and 50.degree. C. to form a second precipitate of sodium bicarbonate; PA1 g) recovering the second precipitate of sodium bicarbonate and recycling recovered second precipitate to step b); PA1 h) conditioning the solution from step g) by at least one of heating the solution to 95.degree. C. to liberate ammonia and carbon dioxide and contacting the solution from step g) with sulfuric acid to degas any carbonate minerals; PA1 i) cooling solution remaining from step h) to a temperature of between -5.degree. C. and 2.degree. C. to form a third precipitate of sodium bicarbonate, and precipitates of sodium sulfate and ammonium sulfate; PA1 j) recovering the third precipitate of sodium bicarbonate and precipitates of sodium sulfate and ammonium sulfate from the solution of step i) and recycling recovered third precipitate and the precipitates of sodium sulfate and ammonium sulfate to step b); PA1 k) treating solution remaining from step j) with sulfuric acid to degas any remaining carbonate minerals from sodium bicarbonate and reducing the sodium sulfate to less than 7% by weight; and subsequently PA1 l) recovering purified ammonium sulfate solution. PA1 a) providing a solution of sodium sulfate; PA1 b) contacting the sodium sulfate solution with carbon dioxide and ammonia or ammonium ions to form a first precipitate of sodium bicarbonate and a solution containing ammonium sulfate; PA1 c) progressively precipitating sodium bicarbonate from the solution to increase the concentration of ammonium sulfate and reduce the concentration of sodium bicarbonate in the solution; PA1 d) recovering as a product the first precipitate of sodium bicarbonate; PA1 e) centrifuging and washing the first precipitate of sodium bicarbonate to convert the sodium bicarbonate into industrial grade sodium bicarbonate; PA1 f) treating solution remaining from d) with sodium sulfate at a temperature of 38.degree. C. to form a second precipitate of sodium bicarbonate; PA1 g) recovering the second precipitate of sodium bicarbonate and recycling recovered second precipitate to step b); PA1 h) conditioning the solution from step g) by at least one of heating the solution to 95.degree. C. to liberate ammonia and carbon dioxide and contacting the solution from step g) with sulfuric acid to degas any carbonate minerals; PA1 i) cooling solution remaining from step h) to a temperature of 2.degree. C. to form a third precipitate of sodium bicarbonate, and precipitates of sodium sulfate and ammonium sulfate; PA1 j) recovering the third precipitate of sodium bicarbonate and precipitates of sodium sulfate and ammonium sulfate from the solution of step i) and recycling recovered third precipitate and the precipitates of sodium sulfate and ammonium sulfate to step b); PA1 k) treating solution remaining from step j) with sulfuric acid to degas any remaining carbonate minerals from sodium bicarbonate and reducing the sodium sulfate to less than 7% by weight; PA1 l) removing precipitates formed in the solution from step k); and PA1 m) recovering purified ammonium sulfate solid. PA1 a) providing a solution of sodium sulfate; PA1 b) contacting the sodium sulfate solution with carbon dioxide and ammonia or ammonium ions to form a first precipitate of sodium bicarbonate and a solution containing ammonium sulfate; PA1 c) progressively precipitating sodium bicarbonate from the solution to increase the concentration of ammonium sulfate and reduce the concentration of sodium bicarbonate in the solution; PA1 d) recovering as a product the first precipitate of sodium bicarbonate; PA1 e) centrifuging and washing the first precipitate of sodium bicarbonate to convert the sodium bicarbonate into industrial grade sodium bicarbonate; PA1 f) treating solution remaining from d) with sodium sulfate at a temperature of between 35.degree. C. and 50.degree. C. to form a second precipitate of sodium bicarbonate; PA1 g) conditioning the solution from step f) by at least one of heating the solution to 95.degree. C. to liberate ammonia and carbon dioxide and contacting the solution from step f) with sulfuric acid to degas any carbonate minerals; PA1 h) cooling solution containing the second precipitation of sodium bicarbonate from step f) to a temperature of between -5.degree. C. and 2.degree. C. to further precipitate of sodium bicarbonate, and form precipitates of sodium sulfate and ammonium sulfate; PA1 i) treating the solution, the precipitate of sodium bicarbonate and the precipitates of sodium sulfate and ammonium sulfate from step h) with sulfuric acid to precipitate remaining sodium bicarbonate; PA1 j) recovering the precipitate of sodium bicarbonate and precipitates of sodium sulfate and ammonium sulfate from the solution of step i) and recycling recovered sodium bicarbonate precipitate and the precipitates of sodium sulfate and ammonium sulfate to step b); and PA1 k) recovering purified ammonium sulfate solution. PA1 a) exposing the stream to oxidizing conditions to generate a sulfur containing compound; PA1 b) contacting the sulfur containing compound with sodium bicarbonate to generate sodium sulfate; and PA1 c) processing the sodium sulfate according to the method of claim 1.
It is clear that the brine is evaporated and that the ammonium sulfate is reacted with the brine to produce sodium sulfate inter alia. The phase equilibria relati onship between the elements present in the system was not recognized.
The teachings of this reference only provide for a closed loop system for a sodium sulfate and ammonium sulfate saturated solution system. This system can only result in the formation of double salt. No other result is possible based on the teachings. The teachings are limited in that it was believed that the solubility difference could yield an ammonium sulfate product. This is incorrect; the result is an ammonium sulfate contaminated system.
In Stiers et al, U.S. Pat. No. 3,493,329, the teachings are directed to the preparation of sodium bicarbonate and hydrochloric acid. This goal is consistent with the teachings of Stiers et al. at column 11 of the disclosure beginning at line 23 through line 43, wherein the following is indicated:
The teachings of the Stiers et al. reference not only are insufficient to direct one to formulate ammonium sulfate in a purity of greater than 75%, but the disclosure is further completely absent of any teaching on how to obtain ammonium sulfate singly. The Stiers et al. reference does not and can not result in the generation of ammonium sulfate as a single product as is clearly possible by the teachings of the present invention.
By following the Stiers et al. methodology, one cannot generate a pure ammonium sulfate product, since the reference completely fails to recognize the limitations of the phase equilibria of the salt system and the combination of steps necessary to overcome the inherent contaminating steps associated with this salt system. Although there is a reference to point A in FIG. 10 of Stiers et al. for the preparation of the product, it is clear that although no double salt is indicated to be in the mixture, there is no indication that the product does not include mixed salt. This is reflected in the disclosure where Stiers et al. indicates that there is simultaneous precipitation of sodium sulfate and ammonium sulfate. This is consistent with the data that Stiers et al. provides as indicated at column 12 beginning at line 21. There is no data presented where the quantity of ammonium sulfate, standing on its own, is set forth. In each case, the data presented is expressed as a proportion precipitated in a compound, i.e, double salt inter alia. Finally, from the text set forth beginning at line 32, Stiers et al. indicates that:
From a review of FIGS. 10 and 11, the fact that no ammonium sulfate is generated singly becomes evident. No data is presented for ammonium sulfate generation; the results from practising this methodology are only a mixed salt and a double salt. Nothing else is obtainable by practising this method.
Finally, Kresnyak et al. in U.S. Pat. No. 5,830,442, issued Nov. 3, 1998, teach an improved process for producing ammonium sulfate. This process is attractive where energy consumption and conversion efficiency are not of primary concern. In this process, sodium sulfate is removed by significant energy input to the evaporators with subsequent cooling. The result is a 2:1 ratio of double salt to solution which then must be evaporated in order to recover ammonium sulfate. As will be appreciated by the skilled process designer, this separation creates difficulties in terms of filtering such a significant amount of precipitated double salt. Further, the process employed the technique of redissolving the double salt and adding this to the evaporator to make sodium sulfate for the recycle stream. This procedure adds to the evaporative load of the process.
In previous attempts to maximize yields and productivity, it was not realized that the initial solution containing the sodium sulfate was undersaturated; this detail is important to perpetuating the reactions involved in synthesizing the ammonium sulfate.
In view of the limitations of the prior art, it is evident that a need remains for a process whereby ammonium sulfate can be formulated in high yield at a high purity using energy efficient unit operations in a proper sequence. The present invention fulfils these objectives in an elegant manner to formulate ammonium sulfate and United States Pharmacopoeia sodium bicarbonate.